Typically, a power take off (PTO) gear is designed to transmit engine torque to various accessories, such as a fire truck water pump or a hydraulic cylinder for a dump truck via a transmission. During idling of an engine for a vehicle housing the transmission, angular fluctuations occur between a PTO at the transmission and the PTO gear. The angular fluctuations cause undesirable audible noise in the PTO gear, for example, an input element of the PTO gear oscillates with respect to an output element, such as a ring gear, causing the input element to bang against the output element. Further, during start-up of the engine undesirable noise occurs when the engine and transmission system, including the PTO gear, are in a resonance condition. For example, the input element can contact the output element at a frequency of about 10 Hz.
Commonly owned U.S. Patent Application Publication No. 2010/0252390 discloses a power take off gear using elastic elements to dampen undesirable vibration associated with the idle condition. However, due to the relatively low spring rate for the elastic elements, the elastic elements do not attenuate the resonance condition or prevent the undesirable noise associated with engine start-up.
Bumper springs have been used in systems where a second damper stage is required. Bumper springs become active when a built in degree of travel is reached. Once bumper springs are engaged the first stage springs work in parallel to the bumper springs resulting in higher capacity. Friction control plates have been used in parallel with a spring package to provide friction at large travel angles. Friction control plates are generally axially loaded plates located parallel to the main torque path made of material with durable wear properties such as high carbon steel or Teflon. The axial load is generated by a diaphragm spring. A defined amount of lash is built into the system so that the friction control plates do not engage until a certain travel is reached.
Both bumper springs and friction control plates can require increased amount of axial and radial space in a design. Bumper springs only provide a fully elastic element without impact absorption characteristics. Thus, the springs capture vibration energy in the system instead of absorbing the energy. The effectiveness of friction control plates is limited by the applied axial force and the number of friction surfaces.